Products

Cetus on Object-Oriented Database Management Systems
Links to evaluations, benchmarks and products.
http://www.cetus-links.org/oo_db_systems_1.html

Choosing the Right OODB Solution
A short comparison of ObjectStore, Versant, Poet, and Objectivity mostly focusing on the evaluation criteria.
http://archive.devx.com/dbzone/articles/sf0801/sf0801-1.asp

ConteXt
An object-based database management system optimized for user interaction instead of transaction processing. It includes a database browser providing secure access to its server across the Internet. C++ binding for several flavours of UNIX. [Source code freely available but not on website.]
http://unixspace.com/context/

Eaglehawk StrongBox
Internet accessible object-oriented database that allows inherently secure remote access to (legacy) data from fixed and wireless devices. Also provides on-line schema evolution and access audit mechanisms.
http://www.eaglehawk.com

eXtremeDB
Main memory database for embedded devices with no need for secondary storage persistency. Provides ACID transactions. Schema compiler generates object-oriented-like interface using C as target language. Available for Win32/Windows CE, QNX, VxWorks, Linux and others.
http://www.mcobject.com

EyeDB
ODMG 3.0 compliant DBMS (including OQL) with manipulatable classes, templates and triggers. Supports multi-database objects. C++ and Java bindings. [Free for educational purposes]
http://www.eyedb.org

Generic Object Oriented Database Management System (GOODS)
Fully distributed ODBMS using a fat client model. The client side includes an adaptation layer to enable language independence and metaobjects to represent different aspects of transactions and caching. Currently only C++ bindings. [Open Source]
http://www.ispras.ru/~knizhnik/goods.html

GigaBASE
Single-node DBMS with SQL-like query language, arrays, computed attributes and a C++ API. [Open Source]
http://www.ispras.ru/~knizhnik/gigabase.html

Orient
ODBMS compliant with the ODMG 3.0 standard. It's available as Just Edition (for small applications) and Enterprise Edition with extra components for replication, load-balancing and fault-tolerance. Supports Windows and Linux. Free Just version available on Web site.
http://www.orientechnologies.com/

ZOPE
The Z Object Publishing Environment consists of an object database (ZODB) and application server (ZServer) written in Python.
http://www.zope.org/

Zope IndexedCatalog
An LGPL extension to the Zope DB that provides indexing and querying.
http://async.com.br/projects/IndexedCatalog